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Showing 10 results for Polarization

Alah Karam S.r., Alah Karam S.r.,
Volume 1, Issue 1 (3-2004)

In this paper redox reaction processes and phase, formation on ternary Pb-2Sn-0.08Ca alloy utilized as insoluble lead anodes in copper electro winning cells, were investigated in 2M H__2SO__4 electrolytes, using cyclic voltammetry technique (CVA). A potential range between - 1.3V to 2.6V was chosen at various scan rates in order to study the anodic behavior and phase composition of the oxide layers on Pb-2Sn-0.08Ca alloy. Potential measurements were carried out with respect to a standard calomel electrode (SCE). The surface examination and phase composition of the lead alloy were determined by electron microscopy analysis (SEM) and x-ray diffraction technique, after- exposure to the cyclic voltammetry tests. The results indicated that the protective oxide layer (Pb0__2) formed at a much slower rate when exposed to 2M H__2SO__4 solutions, whilst its degradation due to a reduction in the applied potential occurred at a much faster rate. Hence, Pb0__2 did not remain stable, when the externally applied potential dropped below 1.SV and as a result, pitting initiated sporadically on the surface of the electrode.
Pakshir M., Amini R.,
Volume 2, Issue 1 (3-2005)

Anodes are critical component of cathodic protection systems. As part of this effort, three different anodes were tested in a cathodic protection system that was designed and constructed to prevent further corrosion of reinforced concrete. This anodic system includes an electrically conductive coating composition applied in fluid form over an outer surface of the concrete mix. The composition further includes a predetermined amount of electrically conductive carbon material (coke, carbon black, graphite) uniformly distributed in the epoxy resin (as a binder) whereby the coating composition has a predetermined value of resistively. This investigation attempts to find the best type and optimum content of conductive carbon filler in poxy coating, to ensure optimal anode working parameters for marine environments (basically marine and sewer environments) and if any of the coating systems tested in this study excel over the other. In this study, electric and electrochemical parameters of three layer (with average coating thickness of 300µm) coke-epoxy, carbon black-epoxy and graphite-epoxy conducting paints (with different amount of filler) have been determined during long-term anodic polarization (70 days) in a seawater solution. During this test, on the basis of impedance measurements, the electrical resistances of these coatings have been calculated every 14 days. if conductive paints exhibit good electric and electrochemical stability, they will be attractive for cathodic protection of reinforced concrete.
Moayed M.h.,
Volume 2, Issue 3 (9-2005)

In this research pitting Corrosion of a sensitized 316 stainless steel was investigated employing potentiodynamic, potentiostatic techniques. Sensitization process was carried out on as-received alloy by submitting the specimen in electric furnace set at 650°Cfor five hours and then the specimen was quenched 25°C water. Potentiodynamic polarization of as received and sensitized specimens in 1M H2SO4 solution at room temperature and 70°C clearly revealed that the sensitization process has caused a magnificent change on electrochemical behavior of the specimen by changing critical current density for passivation, passivation potential and passive current density. Optical microscopy examination of the specimen surface after oxalic acid electrochemical etching also showed the deterioration of grain boundary of sensitized specimen due to chromium carbide precipitation in compared to as-received one. Several anodic potentiodynamic polarization on rode shaped working electrodes prepared from as-received and sensitized specimen in 3.5% NaCl test solution proved an average ~220 mV drop in pitting potential due to sensitization. Anodic potentiostatic polarization at 400 and 200 mV above corrosion potential also demonstrate the deterioration of pitting resistance of alloy as a result of sensitization. Scanning electron microscopy examination of anodically polarized of sensitized specimen at 700mVprior and after oxalic acid etching revealed large stable pits with lacy cover and also openpits with deep crevice for etched specimens.
H. Fattahi, M. H. Shariat,
Volume 5, Issue 1 (3-2008)

Abstract: In chloride salt solutions, titanium alloys exhibit reasonably high pitting potentials as high as +10 V (vs. Ag/AgCl) at room temperatures. On the other hand, anodic pitting potentials are significantly lower in bromide solutions. In this study, pitting corrosion of commercially pure titanium in aqueous NaBr solution of 0.1 M concentration at room temperature was studied and the effect of an external magnetic field oriented both parallel and perpendicular to electrode surface was investigated. Cyclic potentiodynamic and potentiostatic polarization tests were carried out. Anodic breakdown potential of +1.45 V (vs. Ag/AgCl) obtained in the absence of magnetic field, decreasing to +1.11 V in the presence of a 0.05 T parallel magnetic field. The perpendicular magnetic field actually did not affect the breakdown potential. Applying of an external magnetic field, independent of its orientation, shifted the repassivation potential approximately 150 mV in the positive direction. SEM microscopy observations of sample surfaces indicated that applying of magnetic field results in some variations in the pit shapes and their sizes.
N. Eslami Rad*, Ch. Dehghanian,
Volume 7, Issue 4 (10-2010)

Abstract: Electroless Nickel (EN) composite coatings embedded with Cr2O3 and/or MoS2 particles were deposited to combine the characters of both Cr2O3 and MoS2 into one coating in this study. The effects of the co-deposited particles on corrosion behavior of the coating in 3.5% NaCl media were investigated. The results showed that both Ni-P and Ni-P composite coatings had significant improvement on corrosion resistance in comparison to the substrate. Codeposition of Cr2O3 in coating improved corrosion characteristic but co-deposition of MoS2 decreased corrosion resistance of the coating.
M. Vishnudevan,
Volume 9, Issue 4 (12-2012)

Corrosion behavior of mild steel in chloride contaminated alkaline solution has been studied for the period up to 100days. Saturated Calcium hydroxide solution was used as alkaline solution and 0.5M NaCl solution was used to accelerate mild steel corrosion. The Charge transfer resistance Rct, Current density Icorr and inhibition efficiency values were obtained from tafel polarization and electrochemical impedance spectroscopic technique for sodium nitrite, sodium citrate and sodium benzoate mixed inhibitors. The results were compared with nitrite inhibitive system. The combination of nitrite inhibitor along with benzoate and citrate inhibitors enhanced the durability of mild steel through formation of nanosized -Fe2O3 film on steel suface even in presence of high chloride contamination. The results obtained from gravimetric method proved that the 100 days exposure of mild steel in nitrite with citrate, nitrite with citrate and benzoate mixed inhibitors showed the maximum inhibition efficiency of 98% in comparison with nitrite inhibitive system alone (41.5%). The maximum corrosion resistance performance of these mixed inhibitors system was due to the formation of thick layer of nano : Fe2O3 fibrous film on steel surface.
Sh. Shahriari, M. Ehteshamzadeh,
Volume 10, Issue 1 (3-2013)

Abstract: Plasma electrolytic oxidation (PEO) technique was used to prepare ceramic coatings on the casted aluminum alloys containing ~5 and ~9.5 wt.% Mg. The applied voltage was controlled at 450V and 550V for evaluating the effect of this main parameter, as well as, magnesium content of the substrate on the microstructure and electrochemical corrosion behavior after PEO treating. The results of X-ray diffraction confirmed formation of galumina and MgSiO3. It was found that higher applied voltage caused fewer and minor discharge channels which led to higher corrosion resistance. Also, increasing of magnesium content of the substrate caused decreasing of polarization resistance, which could be associated to the formation of MgSiO3.
A. Fattah-Alhosseini, H. Farahani,
Volume 10, Issue 4 (12-2013)

The effects of H2SO4 concentration on the electrochemical behaviour of passive films formed on AISI 304 stainless steel were investigated using by potentiodynamic polarization, Mott–Schottky analysis and electrochemical impedance spectroscopy (EIS). Potentiodynamic polarization indicated that the corrosion potentials were found to shift towards negative direction with an increase in solution concentration. Also, the corrosion current densities increase with an increase in solution concentration. Mott–Schottky analysis revealed that the passive films behave as n-type and p-type semiconductors at potentials below and above the flat band potential, respectively. Also, Mott– Schottky analysis indicated that the donor and acceptor densities are in the range 1021 cm-3 and increased with solution concentration. EIS data showed that the equivalent circuit Rs(Qdl[Rct(RrQr)]) by two time constants is applicable.
Z. Shahri, S. R. Allahkaram,
Volume 10, Issue 4 (12-2013)

Metal matrix nano composite coatings possess enhanced properties such as corrosion and wear resistance. This paper aims to study the corrosion behavior of pure Co and Co-BN nano composite coatings deposited with different particles concentration (5-20 g L-1) on copper substrates using electroplating technique. Morphology and elemental compositions of the coatings were investigated by means of scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS). The corrosion behavior was analyzed in a 3.5 wt% NaCl via polarization and impedance techniques. The results obtained in this study indicate that the co-deposition of BN nano particles improved corrosion resistance of electrodeposited cobalt coatings.
A. Fattah-Alhosseini, M. Ranjbaran, S. Vajdi Vahid,
Volume 12, Issue 2 (6-2015)

In this study, corrosion behaviour of A356-10 vol.% SiC composites casted by gravity and squeeze casting is evaluated. For this purpose, prepared samples were immersed in HCl solution for 1h at open circuit potential. Tafel polarization and electrochemical impedance spectroscopy (EIS) were carried out to study the corrosion resistance of composites. The Tafel polarization and EIS studies of the corrosion behaviour of the A356-10 vol.% SiC composites showed that the corrosion resistance of the composite casted by squeeze casting was higher than that of the composites casted by gravity in selected corrosion media. Also, the Tafel polarization and EIS studies revealed that the corrosion current densities of both composites increase with the increase in the concentration of HCl. The micrographs of scanning electron microscope (SEM) clearly showed the squeeze casting composite exhibits a good dispersion/matrix interface compared to that of the composites produced by gravity casting

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